Semiconductor devices may be designed to interact with electromagnetic radiation that is incident upon a particular area of the device. One such semiconductor device is a spatial light modulator, which serves to redirect the path of incoming radiation by action of one or more accepted principles of optics, such as reflection, refraction, or diffraction. Unfortunately, in many of these devices, some incident radiation may not be redirected in the desired manner due to physical gaps, unwanted diffraction, scattering effects, or other phenomena. Such radiation may be deemed “stray radiation.” This stray radiation may degrade the performance of the overall system if a mechanism of absorbing the radiation is not present.
An example of a spatial light modulator whose performance may be degraded by stray radiation is a digital micro-mirror device (DMD). DMDs, which may be used in a variety of optical communication and/or projection display systems, involve an array of micro-mirrors that selectively communicate at least a portion of an optical signal or light beam by pivoting between active “on” and “off” states. To permit the micro-mirrors to pivot, each micro-mirror is attached to a hinge coupled to a CMOS substrate that controls the movement of the micro-mirrors. Unfortunately, when the micro-mirrors are in the “off” state, the CMOS substrate, which may be optically reflective, is exposed. As light passes between the micro-mirrors of the DMD, the light may then be reflected by the surface of the substrate, resulting in stray radiation that limits the contrast ratio achievable in display systems based on the DMD.
A variety of methods have been employed in an attempt to reduce the reflectivity of the CMOS substrate that makes up the substructure of DMDs and other spatial light modulators. One such method that has been employed is the application of an antireflective and/or absorptive coating to certain regions of the semiconductor device which are physically located on a different plane than the surface(s) responsible for the redirection effects. These coatings, however, are limited in that they may require complicated materials and may not absorb sufficiently within the frequency range of interest to provide the best possible system performance. Additionally, some of these coatings require patterning over the substrate due to optical or electrical performance issues.